Perchlorate appears in the groundwater that 10-20 million Americans could drink; and perchlorate might adversely affect people's thyroid gland. The American Water Works Association Research Foundation (AWWARF) has been charged by Congressional earmark, through the Environmental Protection Agency (EPA), to devise methods for removing perchlorate from groundwater.
Perchlorate (ClO4−) contaminates groundwater that could potentially be used by millions of people in this country. A considerable portion of this contaminated groundwater lies beneath the ground in arid regions of this country, such as California, Nevada; and it also appears in the vicinity of military bases and aerospace companies in states such as New York, Massachusetts, Pennsylvania and numerous others. This presents a large problem because drinking water, especially during the dry summer months, can become extremely scarce.
Perchlorate appears in water because it has been used in rocket propellant, along with ammonia and solid aluminum. In a number of places where rocket propellants have been manufactured, ammonium perchlorate has been discarded on the soil, and then it has percolated into the groundwater. At the concentrations that perchlorate is found in water (i.e., 1-3000 ppb), it does not naturally decompose in a reasonable time frame, if at all. Perchlorate, at high concentrations, is known to affect the thyroid gland, and it is perceived that it may also affect the thyroid gland at trace concentrations. For this reason, the California Department of Health has identified a 4 ppb action level for perchlorate; and this action level may drop yet further. Other states are contemplating action levels as low as 1 ppb.
There are a few commercially available methods for removing perchlorate. One such process is the passing of perchlorate contaminated water through a bed of ion exchange resin. A disadvantage of such ion exchange resin process is that it utilizes a very high concentration of salts (i.e., 35,000 to 70,000 ppm), and sometimes very expensive catalyst material. This can result in the formation of a brine waste solution (i.e., 35,000 to 70,000 ppm) which must then be properly disposed of without causing environmental issues with the surrounding water tables.
There are also some biological processes that have been developed; but by their very nature, they are less acceptable for treatment of drinkable water for humans, due to the use of microorganisms that could include consortia which are known to cause diseases. Few water utilities would accept the potential liability with placing drinking water in contact with a biological species and then distributing this drinking water to the public, without subsequent filtration which requires yet another unit operation.
Still others have proposed using reverse osmosis processes for the removal of perchlorates from water, but the cost of operating such a reverse osmosis facility has made this process commercially undesirable; and it is not clear that reverse osmosis can remove perchlorate down to the action levels that have been established or are contemplated.
The present inventors have uniquely discovered how to both remove perchlorates and other undesirable anions, such as nitrates, chromates, arsenates, and arsenites, and make them available ultimately for destruction by thermally pretreating or chemically preloading granular activated carbons (GACs) prior to use. Once the chemically preloaded or thermally pretreated GAC has reached the end of its useful service life, it can be regenerated either chemically or thermally and made ready for reuse. The present inventors have uniquely discovered that the process of the present invention is capable of removing perchlorates and other anions by a combination of removal and chemical/thermal regeneration with chemicals that are commercially available in large and inexpensive quantities and which are environmentally acceptable; and which are not known to pose health risks.
The granular activated carbon used pursuant to the process of the present invention provides advantages over other technologies for treating groundwater that is contaminated with both perchlorate and trace organic compounds: (a) GAC can be tailored to remove both perchlorate and organic compounds through a single unit operation rather than two unit operations in series, (b) GAC costs perhaps a tenth as much as ion exchange resins on a per-pound basis, (c) GAC can be thermally reactivated, whereas ion exchange resins decompose at thermal reactivation temperatures; and this means that GAC treatment is conducive to the ultimate destruction of perchlorate via brineless means, and (d) GAC treatment is inherently easy to operate and it does not involve the risks that biological processes do, of releasing microorganisms into a water system.